The present invention is in a process and apparatus for separating liquid ash from an exhaust gas which is formed by the combustion of carbonaceous fuels and is at a temperature of from 1200.degree. to 1800.degree. C. at a pressure of from 1 to 100 bars, preferably from 1 to 30 bars, and has an ash content from 0.1 to 60 g/sm.sup.3 (sm.sup.3 =standard cubic meter).
It is known that small coal particles can be suspended in an oxygen-containing gas and combusted in a combustion chamber so that the inorganic components of the coal become available as ash. In dependence on the the nature of the combustor (consisting, e.g., of a slag tap furnace), the fuel and the oxygen content which is presented, a very high combustion temperature may be achieved so that the exhaust gas formed by the combustion leaves the combustion chamber at a temperature of from 1200.degree. to 1800.degree. C. Under these conditions, the ash which is produced by the combustion may be present in a molten, liquid state.
It is also known that high temperature exhaust gases which are produced by a combustion under pressure can desirably be used to generate electric power because the energy content of these exhaust gases can be converted to electric power by a gas turbine with very high efficiency. The remaining heat content of the combustion exhaust gas leaving the gas turbine can desirably be used to produce steam in a steam boiler. For this reason it is desirable from the aspects of energy and economics to produce combustion exhaust gases which are under pressure and at a temperature which is as high as possible; that temperature lies between 1200.degree. and 1800.degree. C. The production of such a combustion exhaust gas involves the disadvantage that the ash which is formed by the combustion of coal becomes available in a liquid rather than solid state. Before the hot combustion exhaust gas is used in a gas turbine it is necessary to remove substantially all of the liquid ash from the combustion exhaust gas because the gas turbine would otherwise be destroyed by the deposited and solidified ash droplets.
Published German Application 3,720,963 proposes a process wherein ash which is formed by the combustion of coal with air and which is in a pressurized combustion exhaust gas at a temperature from 1200.degree. to 1700.degree. C. is separated from the gas by passing that ash containing gas through at least one porous and gas-permeable ceramic filter element disposed in the combustion chamber. The filter consists mainly of Al.sub.2 O.sub.3, SiO.sub.2, MgO and/or ZrO.sub.2.
It has been found that the life of the ceramic filters is limited particularly treating an exhaust gas from the combustion of relatively high ash content coal. For this reason it is an object of the invention to provide a process which is of the kind described first hereinbefore and which uses simple technical means but which results in a separation at a constant rate for the longest period possible.